Normally, in internal combustion engines that burn natural gas, the spark plug is received by a pre-combustion chamber. The gas is fed into the pre-combustion chamber, and the ignited gas enters the cylinder when the piston is at top dead center to initiate the power stroke for that piston. The use of a pre-combustion chamber improves combustion stability within the engine, for instance.
FIG. 1 is a view of the prior art design. The pre-combustion chamber 10 has a generally cylindrical shape with an exit port 12 that is specifically oriented with regard to the cylinder where the piston reciprocates. The chamber has a flange 14 that rests on a shoulder 16 that surrounds a receptacle or opening in the cylinder head 20. A retaining ring 18 is attached to the cylinder head 20 via thread 22 that extends into the opening in the head 20. After the ring 18 is threaded using a tool that engages internal notches (not shown), a cover 24 is threaded into the same thread 22 in the head 20. Cover 24 has a receptacle 26 with a thread 28 to accept a spark plug 30. A passage 32 leads into chamber 10 to allow fuel, such as natural gas to enter when the plug 30 is fired. The combusted fuel leaves through port 12 to enter the cylinder for the power stroke of the piston (not shown).
The problem with the prior design just described occurs when it is time to remove the cover 24 and extract the retaining ring 18. Both of these items need to be removed to get the chamber 10 out of the head 20. The problem is that removal can become problematic as either the ring 18 or the cover 24 can get stuck on thread 22. If the thread 22 is damaged during this removal, the entire head 20 may require complete replacement. Because these engines can be quite large, the delay in obtaining another head can be lengthy. Moreover, the expense of replacing the head 20 can also be significant. The problem is aggravated by the enormous heat repeatedly generated in the vicinity of the spark plug, which over time seemingly fuses the thread 22 to the head 20 making disassembly difficult without damaging the head 20. In addition, the ring 18 and the cap 24 operate under a predetermined torque, which when combined with the heat cycling and exposure to combustion products and deposits aggravates the removal process. These chambers are a component that must be periodically replaced and it is desirable to be able to remove these chambers without damage to the head 20.